The invention relates to a method and apparatus for ventilating a vehicle interior, which can be switched between an incoming-air operating mode and a circulating-air operating mode, in reference to detection of harmful gases.
For simplicity, the term "circulating-air operation" as used herein also includes an operating situation with a switched-off fresh-air operation without active circulation of the air of the vehicle interior. That is, the invention is also suitable for vehicles which do not have devices for active circulation of the air of the vehicle interior with the incoming air blocked (when the fresh-air supply is blocked).
U.S. Patent Document U.S. Pat. No. 5,320,577 discloses a method and apparatus of this generic type, in which a first gas sensor based on WO.sub.3 is used to measure the concentration of diesel exhaust gas (specifically nitrogen oxides), and a second gas sensor based on SnO.sub.2 is used to measure the concentration of flammable fuel vapors (specifically of hydrocarbons and carbon monoxide) contained therein. The two sensor output signals are analyzed in a special manner based on a calculation of the first and the second time derivatives. Circulating air operation is adjusted when the second derivative of the output signal of the CO and HC sensor is at least as large as a first threshold value, or when the second derivative of the output signal of the NO.sub.x -sensor is smaller than or equal to a negative second threshold value and simultaneously the second derivative of the CO and HC sensor is at least as large as a third threshold value. In each case, circulating air operation is maintained for a time period which is determined as a function of the absolute value of the height and width of the pertaining maximum of the time derivative of the CO and HC sensor signal, or analogously of the value, the height or the width of the pertaining minimum of the time derivative of the NO.sub.x, sensor signal.
German Patent Document DE 29 41 305 A1 discloses an arrangement for ventilating a vehicle interior which contains an outside (that is, an incoming-air) sensor, as well as a vehicle-interior sensor for measuring the harmful-substance concentrations of the outside air and of the inside air. The two measured harmful-substance concentration values are compared with respective threshold values, and the ventilation of the interior is control based thereon.
German Patent Document DE 42 17 394 A1 describes a process for ventilating a vehicle interior in which the harmful-substance concentration of the outside air is determined by a sensor, while the harmful-substance concentration of the inside air is computed by means of a model equation. The air quantity in the vehicle interior, the CO.sub.2 entering from the outside, the CO.sub.2 entering from the occupants and the CO.sub.2 exiting to the outside are taken into account in a special manner. Alternatively, the CO.sub.2 concentration in the interior is measured by means of a CO.sub.2 -sensor. As far as the occurrence of different harmful gases is discussed there, a weighting of the latter is suggested according to their effect on the human organism, and a single weighted harmful substance concentration value which represents the different harmful gases is then obtained.
An interruption of the fresh air supply (that is, a switch-over from incoming air operation to circulating air operation) in the sense of the present invention is triggered when the time variation of the sensor signal has reached or has fallen below a threshold value. The fresh air supply can then be re-opened as soon as the difference between the actual sensor signal value and the sensor signal value during the interruption of the fresh air supply, divided by the last-mentioned signal value, has reached or exceeded a second definable negative threshold value. The two threshold values vary as a function of the harmful-substance concentration of the inside air determined by way of the model equation, and are used to adjust the air.
One object of the invention is to provide a method and apparatus of the initially mentioned type for ventilating a vehicle interior, which permit, at relatively low expenditures, a switch-over between incoming air operation and circulating air operation, which can be individually adapted to various harmful gases, and can also respond to low concentrations of specific harmful gases.
This and other objects and advantages are achieved by the method and apparatus according to the invention, which provides several sensors, one for measuring the incoming-air concentrations of each one of various harmful gases. Operating mode control devices determine the interior concentration of each of these harmful gases individually, without requiring interior harmful gas sensors. The latter determination is made by continuous estimation, based on the harmful gas concentrations measured on the incoming air side, and on the incoming air flow rate (that is, the fresh air quantity per unit time which is guided into the vehicle interior). In this manner, the expenditures for the vehicle-interior-side harmful gas sensors can be eliminated.
The operating mode control devices evaluate the harmful gas concentration, measured on the incoming air side, separately for each of the harmful gases, and generate either an incoming air operation request or a circulating air operating request. The latter signals are evaluated in a logical OR-addition, and a circulating air operation adjustment command is generated if the evaluation of at least one of the harmful gases results in a circulating air operation request. The circulating air operation adjustment command, which is optionally linked to the existence of additional conditions, will then trigger an adjustment of the circulating air operation. Specifically, during an incoming air operation phase the operating mode control devices will generate the circulating air operation adjustment command if the estimated vehicle-interior concentration of at least one of the harmful gases rises at a rate which is above a definable threshold value. This switch-over criterion implicitly also takes into account the incoming-air concentration of the concerned harmful gas, because it enters into the estimation of the vehicle-interior harmful gas concentration.
By evaluating the harmful gas concentrations individually for each harmful gas, those specific harmful gases can also appropriately be taken into account which, compared with other harmful gases, occur in a lower concentration but have a comparably damaging influence. The logic combination of the evaluation results for the individual harmful gases ensures that a switch to circulating air operation is performed even though it is indicated by only one of the several harmful gases.
In one embodiment of the invention the operating mode control devices are designed so that, during circulating air operation, they continuously increase the vehicle-interior concentration of the respective harmful gas by a definable increment in order to estimate the deterioration of the air quality of the vehicle interior, in a simple and appropriate manner and without the requirement that it be detected by sensors. A switch-over command to incoming air operation is generated by the operating mode control devices when all estimated incremented harmful gas concentrations during a definable suitable waiting period are higher than the associated measured incoming-air harmful gas concentrations. The suitable waiting period prevents undesired brief switch-overs to incoming air operation followed by an immediate back to circulating air operation.